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PubMed1999

Collapse and massive pulmonary edema secondary to thrombosis of a mitral mechanical heart valve prosthesis during low-molecular weight heparin therapy.

Mechanical heart valves (MHV) are particularly exposed to thrombosis if anticoagulation becomes ineffective. Thromboembolic complications may be avoided by oral anticoagulation with vitamin K antagonists or derivatives of unfractionated heparin. A few cases of low-molecular weight heparin (LMWH) as sole anticoagulant in patients with MHV have been published, though with contradictory results. We report a case of a massive thrombosis of a St. Jude Medical mitral valve after the patient had been treated for one month with calcium nadroparin (Fraxiparine).

Aged↗
PubMed1991

Stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position.

In this paper, a finite element analysis of the stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position is presented. The geometry of the valve was modified from a relationship proposed by Ghista and Reul (J. Biomechanics 10, 313-324, 1977). The effects of variations in stent height, leaflet thickness and coaptation area on the stress distribution were also analyzed. Analyses were performed with both rigid and flexible stents for the trileaflet valve in order to delineate the effect of stent flexibility on the leaflet stress distribution. The results showed that regions of stress concentration were present near the commissural attachment similar to those predicted with the bioprostheses. The stresses on the leaflets were reduced by increasing the stent height with both rigid and flexible stents. Selectively increasing the leaflet thickness near the commissures and also increasing the coaptation area did not prove to reduce the leaflet stresses when the stent flexibility was taken into account. The possible effect of high stresses on the structural integrity of polyurethane leaflets and its relationship with calcification is yet to be investigated.

Heart Valve Prosthesis↗
PubMed1990

[Reoperations after insertion of heart valve prosthesis].

The authors analysed 167 repeated operations after heart valve prosthetics, which were conducted from 1978 to 1988. The operations were undertaken for the second time mainly in a severe contingent of patients. The reasons for the repeated operations were specific complications according to which 2 groups of patients were set apart: with dysfunction of the prosthesis of noninfectious origin and with prosthetic endocarditis. Study showed that repeated operative intervention undertaken in time reduces considerably its risk and produces a stable positive effect in most cases.

Adolescent↗
PubMed1991

Static and dynamic stresses during valve closure of a bileaflet mechanical heart valve prosthesis.

The effect of contact geometry and component compliance on the magnitude, distribution, and state of various types of stresses on a bileaflet mechanical heart valve prosthesis during valve closure was analyzed using an Edwards-Duromedics mitral valve as example. Static and dynamic stresses developing on both the leaflet and pivot ball during valve closure were modeled using finite element analysis (FEA). Uniform contact between the leaflet and housing as well as between the pivot ball and pivot slot can significantly reduce both static and dynamic stresses around the contact area. The level of the dynamic flexural stresses can be an order of magnitude higher than that of the static stresses. When both the radial and axial compliance of the housing are taken into consideration, peak dynamic stress was more than 40% less than that generated through the impact between a moving leaflet and a non-compliant rigid housing.

Compliance↗
PubMed1997

Nineteen-millimeter aortic St. Jude Medical heart valve prosthesis: up to sixteen years' follow-up.

UNLABELLED: BACKGROUND; Prosthetic valve replacement in a small aortic root without annulus enlargement raises concern about its long-term benefits. METHODS: Between July 1979 and June 1994, 104 (18%) of 593 patients underwent aortic valve replacement using the 19-mm St. Jude Medical heart valve prosthesis. There were 93 women and 11 men, with a mean age of 66.2 +/- 10.6 years. Forty-four patients (42%) were 70 or more years old. The mean body surface area was 1.61 +/- 0.16 m2 (range, 1.2 to 2.1 m2). Forty-nine patients (47%) underwent concomitant procedures; 23 patients (22%) required coronary artery bypass grafts and 25 patients (24%), mitral valve replacement. Ninety-eight patients (94%) presented in New York Heart Association class III and IV. RESULTS: The operative mortality was 7.6% (8 patients). Follow-up was 100% with a mean of 5.48 +/- 3.73 years (range, 1 to 16 years) and a total of 708 patient-years. There were 18 late deaths, with a mortality of 2.5% patient-years. The incidence of thromboembolism was 0.4% patient-years (3 patients) and anticoagulant-related morbidity was 0.85% patient-years (6 patients). Long-term survival in the two groups with a body surface area of less than 1.7 m2 and 1.7 m2 or more was not statistically different (p = 0.30). The univariate analysis with body surface area as a predictor of mortality showed that a larger body surface area had no effect on the long-term mortality (chi2 p value = 0.36). Survival for 5 and 10 years with the 95% confidence interval was 80.6% +/- 8.3% and 61.6% +/- 15%. Freedom from thromboembolism was 96.3% +/- 4.2% and anticoagulant-related hemorrhage was 91.8% +/- 6.8% at the end of 16 years. Cox proportional hazards model, with time-dependent covariates, showed that events of thromboembolism, anticoagulant-related hemorrhage, and myocardial infarction during follow-up increased the risk of late death (risk ratio, 9.5, 10.3, and 32.8, respectively). The age at operation was an independent risk factor, with decreased survival with age 70 or more years (p = 0.0002). However, body surface area (p = 0.97) and concomitant cardiac procedures (p = 0.86) were not statistically significant predictors of death. CONCLUSIONS: The long-term performance of the 19-mm St. Jude Medical heart valve prosthesis in the small aortic root is satisfactory irrespective of the body surface area, and it is a viable alternative for such patients.

Adult↗
PubMed1994

Transient behavior analysis of a mechanical monoleaflet heart valve prosthesis in the closing phase.

In this paper, an analysis of the dynamics in the closing phase of the occluder of a mechanical monoleaflet heart valve prosthesis is presented. The dynamic analysis of the fluid in the vicinity of the occluder was based on the control volume approach. The backflow velocity of the fluid was computed by applying the continuity and momentum equations in the unsteady state. By considering the fluid pressure and gravity as external forces acting on the occluder, the moment equilibrium on the occluder was employed to analyze the motion of the occluder during closing and the force of impact between the occluder and the guiding struts. The computed magnitudes of the occluder tip velocities, as well as the backflow of the fluid during the closing phase using this model, were in agreement with previously reported experimental measurements. The maximum impact force between the occluder and guiding struts of 140-280 N was determined to occur during the initial impact for a duration of 35-45 microseconds. The results of such model studies may be extended for the analysis of the endurance limit of the valve prostheses as well as to determine the mechanical stresses on the formed elements and the incipience of cavitation bubbles during the closing phase of the valve function.

Biomechanical Phenomena↗
PubMed1997

The Bicarbon heart valve prosthesis: short-term results.

BACKGROUND AND AIMS OF THE STUDY: To determine the short-term results of the Bicarbon (Sorin Biomedica, Saluggia, Italy) heart valve prosthesis at our institution. METHODS: Between November 1991 and December 1995, 256 patients (mean age 59.9 +/- 9.8 years) underwent valve replacement with a Bicarbon valve prosthesis. The mean ejection fraction was 60 +/- 14.8% and the mean left ventricular end-diastolic pressure 15.9 +/- 8.7 mmHg. Redo (n = 61) and combined procedures (n = 72) were included in this study; mixed types of prostheses were excluded. The procedures were divided into groups: aortic valve replacement (n = 163), mitral valve replacement (n = 60) and aortic-mitral (double) valve replacement (n = 33). Kaplan-Meier survival analysis was performed and predictors for survival were tested univariately and multivariately. RESULTS: The mean follow up was 30 +/- 25.1 months with a total of 7,696 patient-months (641.3 patient-years) and was 100% complete. The Kaplan-Meier survival rate at 48 months was 87 +/- 2%. The valve-related morbidity expressed as linearized incidence rate (% per patient-year) was: anticoagulation bleeding 2.3 +/- 0.6; thromboembolic event 1.0 +/- 0.4; periprosthetic leak 0.6 +/- 0.3; and endocarditis 0.3 +/- 0.2. Univariate significant factors for worse survival were: higher preoperative New York Heart Association (NYHA) functional class, valve implantation site, presence of associated operation, increasing age, decreasing ejection fraction, longer aortic cross-clamp time, and longer cardiopulmonary bypass time. In multivariate analysis longer aortic cross-clamp time and higher preoperative NYHA classification were significant independent predictors. CONCLUSIONS: These good short-term results after Bicarbon valve replacement are encouraging and comparable with those obtained with other bileaflet mechanical heart valves. However, further follow up is mandatory.

Adult↗
PubMed2002

[Anticoagulation in patients with heart valve prosthesis].

The growing number of recipients of artificial heart valves draws ever more frequent attention to the problem of anticoagulant therapy, not only in its daily management but also in the event of specific conditions such as pregnancy, extra-cardiac surgery and invasive cardiac procedures in which specific measures must be adopted. In each case it is necessary to take into account not only the characteristics of the individual prosthesis but also those of the individual patient, each time making an overall assessment of the specific thromboembolic risk without forgetting possible complications of hemorrhage. This review examines the various mechanisms underlying the thromboembolic risk and, in the light of the leading literature on the topic, seeks to identify the most appropriate behaviors to adopt in the management of each individual case.

Anticoagulants↗
PubMed1996

Cavitation dynamics of medtronic hall mechanical heart valve prosthesis: fluid squeezing effect.

The cause of cavitation in mechanical heart valves is investigated with Medtronic Hall tilting disk valves in an in vitro flow system simulating the closing event in the mitral position. Recordings of pressure wave forms and photographs in the vicinity of the inflow surface of the valve are attempted under controlled transvalvular loading rates averaged during valve closing period. The results revealed presence of a local flow field with a very high velocity around the seat stop of mechanical heart valves that could induce pressure reduction below liquid vapor pressure and a cloud of cavitation bubbles. The analysis of the results indicates that the "fluid squeezing" between the stop and occluder as the main cause of cavitation in Medtronic Hall valves. The threshold loading rate for cavitation initiation around the stop was found to be very low (300 and 400 mmHg/s; half the predicted normal human loading rate that was estimated to be 750 mmHg/s) because even a mild impact created a high speed local flow field on the occluder surface that could induce pressure reduction below vapor pressure. The present study suggests that mechanical heart valves with stops at the edge of major orifice region are more vulnerable to cavitation, and hence, have higher potential for damage on valve components and formed elements in blood.

Blood Flow Velocity↗
PubMed1980

[Sinus rhythm restoration in atrial fibrillation after heart valve prosthesis in rheumatic defects].

The rehabilitation program for patients who underwent heart valve prosthetics must include restoration of the sinus rhythm. On the basis of the results of electric-pulse therapy and quinidine therapy in 88 patients, it is shown that the first method is more effective than the second, but in view of the sufficient efficacy and safety of quinidine therapy with the use of medium daily doses (not more than 2 g) it may be used in some of the patients. It is advisable to restore the sinus rhythm in periods of 3 months to 3 years after operation on the heart. Restoration of the sinus rhythm improves the general condition of patients after heart valve prosthetics, normalizes hemodynamics, increases the physical capacity for work considerably, and provides greater possibilities for the return of convalescents to their jobs.

Atrial Fibrillation↗
PubMed1979

[Sanatorium stage in the rehabilitation of patients with rheumatic defects after heart valve prosthesis].

In 93.2% of 104 patients treated at a cardiological sanatorium after heart valve prosthetics the condition had improved by the time of discharge and only in 2.9% (3 patients) it had grown worse. The measures of rehabilitation comprised curative, physical, and psychologic aspects. The improvement in the condition of patients who had been operated on was attested by the results of ECG, polycardiography, and external respiration tests. The increased tolerance to physical load and the improved ability for coping with the tasks of every-day life are also objective indicators of the effectiveness of the stage of sanatorium treatment in the general complex of rehabilitation of patients who had been subjected to heart valve prosthetics.

Adolescent↗
PubMed2006

CFD simulation of a novel bileaflet mechanical heart valve prosthesis: an estimation of the Venturi passage formed by the leaflets.

The aim of this study was to validate the flow characteristics of the novel Helmholtz-Institute Aachen Bileaflet (HIA-BL) heart valve prosthesis. The curved leaflets of the HIA-BL valve form a Venturi passage between the leaflets at peak systole. By narrowing the cross section the flow accelerates and the static pressure at the central passage decreases according to the Venturi effect. The low-pressure zone between the leaflets is expected to stabilize the leaflets in fully open position at peak systole. To investigate the Venturi passage, the flow fields of two valve geometries were investigated by CFD (Computational Fluid Dynamics): one geometry exhibits curved leaflets resulting in a Venturi passage; the other geometry features straight leaflets. The flow profiles, pressure distribution and resulting torque of both passages were compared and investigated. Although flow profiles downstream of both valves were similar, the flow passages between the leaflets were different for the investigated leaflet geometries. The straight leaflet passage showed a large boundary layer separation zone near the leaflets and the lowest pressure at the leading edge of the leaflet. The Venturi passage showed a reduction of the boundary layer separation zones and the lowest pressure between the leaflets could be found in the narrowest flow cross section of the Venturi passage. Additionally, the resulting torque showed that the Venturi passage produced an opening momentum. The results demonstrate that the Venturi passage stabilizes the leaflets in open position at peak systole.

Blood Flow Velocity↗
PubMed2004

Mechanical heart valve prosthesis in the pulmonary position without anticoagulation: case report.

A 10-year-old girl underwent tetralogy of Fallot (TOF) repair and subsequent pulmonary valve replacement with a St. Jude Medical mechanical heart valve prosthesis. Valve replacement was necessary due to right heart failure resulting from pulmonary regurgitation occurring three months after TOF repair. At the age of 25 years, when she became pregnant, routine cardiac evaluation indicated that she had not used oral anticoagulation during the past 15 years. The patient was of rural origin, and of poor socioeconomic status, but is currently in her 15th postoperative year, with neither clinical problems nor any sign of valve failure.

Adult↗